Long-Term Highly Stable High-Voltage LiCoO2 Synthesized via a Solid Sulfur-Assisted One-Pot Approach.

Commercialized lithium cobalt oxide (LCO) only shows a relatively low capacity of ≈175 mAh g-1 despite a high theoretical capacity of ≈274 mAh g-1 . As an effective and direct strategy, increasing its charge cutoff voltage can, in principle, escalate the capacity, which is however precluded by the irreversible phase transition, oxygen loss, and severe side reactions with electrolytes normally. Herein, an in situ sulfur-assisted solid-state approach is proposed for one-pot synthesis of long-term highly stable high-voltage LCO with a novel compound structure. The coating of coherent spinel Lix Co2 O4 shells on and the gradient doping of SO4 2- polyanions into LCO are in situ realized simultaneously in terms of gas-solid interface reactions between metal oxides and generated SO2 gas from sulfur during synthesis. At 4.6 V, this LCO shows the discharge capacities of 232.4 mAh g-1 at 0.1 C (1 C = 280 mA g-1 ), 215 mAh g-1 at 1 C and 139 mAh g-1 even at 20 C and the capacity retentions of 97.4% (89.7%) after 100 (300) cycles at 1 C. This approach is facile, low-cost and up-scalable and may provide a route to improve the performance of LCO and other electrode materials greatly.

Lithium Antievaporation-Loss Engineering via Sodium/Potassium Doping Enables Superior Electrochemical Performance of High-Nickel Li-Rich Layered Oxide Cathodes.

Low-cost Mn- and Li-rich layered oxides suffer from rapid voltage decay, which can be improved by increasing the nickel content to derive high nickel Li-rich layered oxides (HNLO) but is normally accompanied by reduced capacity and inferior cycling stability. Herein, Na or K ions are successfully doped into the lattice of high nickel Li-rich Li1.2-xMxNi0.32Mn0.48O2 (M = Na, K) layered oxides via a facile expanded graphite template-sacrificed approach. Both Na- and K-doped samples exhibit excellent rate capability and cycling stability compared with the un-doped one. The Na-doped sample shows a capacity retention of 93% after 200 cycles at 1C, which is quite outstanding for HNLO. The greatly improved electrochemical performances are attributed to the increased effective Li content in the lattice via Li antievaporation-loss engineering, the expanded Li slab, the pillaring effect, the increased C2/m component, and the improved electronic conductivity. Different performances by the introduction of sodium and potassium ions may be ascribed to their different ionic radii, which give rise to their different doping behaviors and threshold doping amounts. This work provides a new idea of enhancing electrochemical performance of HNLO by doping proper alien elements to increase the lattice lithium content effectively.

Cobalt/nitrogen codoped carbon nanosheets derived from catkins as a high performance non-noble metal electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction.

Novel energy devices which are capable of alleviating and/or solving the energy dilemma such as overall water splitting and fuel cells require the development of highly efficient catalysts, especially cheap high performance non-precious metal (NPM) catalysts. Here, we prepare highly efficient NPM catalysts of cobalt and nitrogen codoped carbon nanosheets (Co/N-CNSs) for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) using harmful environment-polluting waste of biomass catkins as carbon precursors via a mild mechanical exfoliation and chemical process which is facile, low-cost, environmentally friendly and up-scalable. Compared with a commercial platinum-based catalyst (commercial 20% Pt/C), the Co/N-CNS electrocatalysts show outstanding ORR activity, acceptable HER activity and long term stability with an onset potential of 0.92 V versus the reversible hydrogen electrode (vs. RHE) and a half-wave potential of 0.83 V vs. the RHE in alkaline electrolytes. The excellent performance is closely related to the presence of abundant CoN x active sites. This work offers a novel and effective approach for preparing highly efficient ORR and HER NPM electrocatalysts from waste biomass materials.